Prince William and the Duchess of Cambridge with Prince George at his christening in October 2013. Photograph: John Stillwell/AFP/Getty Images

Australia is holding up changes to the royal succession laws that would end the practice where sons take precedence over daughters, a British government minister said on Wednesday.

The 16 Commonwealth realms which share the same royal family – including Britain, Australia, Canada, New Zealand and Jamaica – must all pass an identical law before the changes can come into effect, unless UK legislation covers it for them.

They have all done so except Australia, said Jim Wallace, the deputy leader of the House of Lords.

The measures mean newborn male children would no longer overtake elder sisters in the line of succession.

Commonwealth realms rushed to agree the changes after Prince William – the elder son of Prince Charles and next in line to the throne after his father – married in April 2011.

They were agreed in principle by prime ministers of the 16 countries at a Commonwealth summit in Perth, Australia 28 October 2011.

The new laws will apply to any descendents of Charles. They can only come into effect when all realms have ratified the change.

Questioned in the House of Lords as to whether any realm might default on the Perth agreement, Wallace told peers: “The intention is that when all 16 realms have agreed or put in place the necessary legislation there will be a simultaneous order to give effect in each of the realms.

“All realms that took the view that legislation is required have passed the necessary legislation apart from Australia.”

He said the six Australian states would legislate first before Canberra does.

“To date, three states have enacted legislation, two have introduced legislation and one, South Australia, has yet to introduce legislation but it is in the middle of an election campaign,” he added.

The law change must be unanimous and identical in each realm to avoid the possibility of ending up with different monarchs in different countries.

In other changes, the new law would also state that anyone marrying a Roman Catholic no longer loses their place in the line of succession.

However, Catholics themselves remain excluded – the sovereign must be in communion with the Church of England.

The new laws would also limit the number of those in the line needing the monarch’s permission to marry to six.